1. Technical Field
The present invention relates to an optical modulator module, more specifically, to a miniature optical modulator module employing a flexible printed circuit board for a portable device.
2. Description of the Related Art
A micro-machine refers to a miniature machine indiscernible with naked eyes. It can also be called a micro electro mechanical system (MEMS), and mainly fabricated by semiconductor manufacturing technology. These micro-machines are applied in information devices such as a magnetic and optical head by using micro-optics and limitation elements, and also applied in the bio-medical field and the semi-conductor manufacturing process by using various micro-fluidics. The micro-machines can be divided based on their function into a micro-sensor, a micro-actuator and a miniature machine.
The MEMS can also be applied in optics. Using MEMS technology, optical components smaller than 1 mm may be fabricated, by which micro optical systems may be implemented.
Conventional optical systems are comprised of a mirror, and a lens mounted on a large and heavy optical bench. The size of the lasers is also large. Significant effort is required in arranging an optical axis, reflection angle and reflection surface to obtain better performance. However, the micro-miniature optical system using MEMS technology reduces such space and efforts, and will show advanced performance.
Micro optical components belonging to the micro-miniature optical system such as a micro-mirror, a micro-lens, and the like are applied in telecommunication devices, display devices and recording devices, due to such advantages as quick response time, low level of loss, and convenience in layering and digitalizing.
As display technologies have advanced, the demand on large screen display devices has grown. The majority of current large screen display devices (mainly projectors) are using liquid crystals as a light-switcher. Such a liquid crystal projector has been popular due to the fact that it is smaller, cheaper, and has a simpler optical system than a CRT projector. However, in the liquid crystal projector, an amount of light is lost while passing through a liquid crystal panel and also projected to a screen. A micro-machine such as an optical modulator element using reflection is employed to reduce such light loss, by which brighter images are obtained.
Also, the demand for portable devices having advanced multi-media functions is increasing to play games or to enjoy DMB broadcast while traveling. The portable devices refer to small size electronic devices designed to be conveniently carried so as to be used for games and mobile communication. The portable device includes a mobile communication device, a PDA (personal digital assistant) and a PMP (personal multimedia player).
A diffraction type optical modulator element having micro-mirrors may be employed as a micro-miniature optical system in the portable device. In general, a conventional diffraction type optical modulator element has been manufactured in hybrid form, because modularizing by building a driving integrated circuit on a separate substrate produces a higher yield and is more cost-effective than integrating the driving integration circuit on the same die.
However, due to the fact that the conventional diffraction type optical modulator element, unlike other elements, uses light, the modularizing process for the diffraction type optical modulator element should be specialized from existing modularizing processes.
Besides, the micro-mirror of the conventional diffraction type optical modulator element is so weak to moisture that it should be seal packed, and the micro-mirror should be designed to discharge heat generated while the light is illuminated and the element is operating to the outside to stabilize its operation and to enhance its durability.
In FIGS. 1A and 1B are illustrated an optical modulator module for solving the aforementioned problems.
FIG. 1A is a plan view of a conventional optical modulator module, and FIG. 1B is an exploded perspective view of the conventional optical modulator module.
As shown in FIGS. 1A and 1B, the optical modulator module comprises an optical modulator element 10, a transparent substrate 20, driving integrated circuits 30a to 30d and a printed circuit board 40. The optical modulator module may further comprise a heat discharging plate and/or a connector.
A lower side of the transparent substrate 20 is attached to the printed circuit board 40. The optical modulator element 10 is attached to an upper side of the transparent substrate 20 in correspondence to a hole 45 formed on the printed circuit board 40.
The optical modulator element 10 modulates incident light inputted through the hole 45 and the transparent substrate 20, and sends out the modulated light. The optical modulator element 10 is connected by flip-chip bonding on the transparent substrate 20. The optical modulator element 10 is sealed from the outer environment since an adhesive is applied around its circumference. The optical modulator element 10 is electrically connected due to an electric wiring distributed along the surfaces of the transparent substrate 20.
The driving integrated circuits 30a to 30d are connected by flip-chip bonding near the optical modulator element 10 attached to the transparent substrate 20, and supply the optical modulator element 10 with driving power according to control signals inputted from the outside.
A first circuit pattern 21 is formed between a lower metallic pad of the optical modulator element 10 and a lower pad for the driving integrated circuit so as to transmit electric signals outputted by the driving integrated circuits 30a to 30d through the lower metallic pad to the micro-mirror of the optical modulator element 10.
A second circuit pattern 23 is formed between a lower pad for the driving integrated circuit and a wire bonding pad 22 of the transparent substrate 20 so as to transmit electric signals inputted through the wire bonding pad 22 from the printed circuit board 40 to the lower pad for the driving integration circuit.
A wire bonding pad 31 on the printed circuit board 40 is wire-bonded to the wire bonding pad 22 of the transparent substrate 20, thereby transmitting electric signals.
Since the printed circuit board 40 is made of a rigid printed circuit board, the optical modulator module illustrated in FIGS. 1A and 1B is inflexible. This inflexibility makes it difficult to mount the optical modulator module on a space smaller than the printed circuit board 40.